A timeline for Dawn's launch
Posted by Emily Lakdawalla
02-07-2007 16:41 CDT
I'm waiting impatiently for the results of tomorrow's launch readiness review for the Dawn mission. I'm keeping my fingers crossed that they've gotten all those nagging problems solved and will be ready to go on Saturday, July 7.
They're certainly making progress preparing the spacecraft for launch. As I was checking the Kennedy Media Center just now they added a few more photos, showing the spacecraft and its upper stage motor being encased in the aerodynamic fairing that will enshroud them both for their journey up through Earth's atmosphere.In preparation for covering the launch events, I've distilled the time information from the mission's press kit and from Marc Rayman's last Dawn Journal into this table, which you might find handy if you plan to follow along. Stay tuned for more Dawn news!
|Time (EDT)||Time (UTC)|
The launch window is about 27 minutes long. At liftoff, the first stage of the rocket and six of the nine solid rocket boosters ignite.
|First six solid rocket boosters burn out|
The first stage of the rocket is still firing as the six solids burn out at an altitude of 24 kilometers (15 miles).
|Remaining three solid rocket boosters ignite||0:02.0||1:19.0||16:10:50||20:10:50|
|Burned-out solids separate|
This happens as the first stage and three solids continue to fire. The separation of the six burned-out solids happens three at a time, with one second elapsing in between the separation events.
|Remaining three solids burn out||1:14.5||2:35.0||16:12:06||20:12:06|
|Remaining solids separate|
The last of the solid rocket boosters fall off as the rocket passes through an altitude of 73 kilometers (45 miles).
|First stage shutoff||1:43.5||4:23.0||16:13:54||20:13:54|
|First stage separation||0:08.0||4:31.0||16:14:02||20:14:02|
|Second stage ignition||0:05.0||4:36.0||16:14:07||20:14:07|
|Payload fairing jettison|
At an altitude of 135 kilometers (84 miles), the nose cone of the rocket splits in half and falls away, and the Dawn spacecraft is exposed to space for the first time.
|Second stage shutdown|
There is a pause in the middle of the firing of the second stage; the spacecraft coasts until it has reached exactly the right position in Earth orbit to begin the journey to Vesta via Mars.
|Second stage restart||9:07.0||18:05.0||16:27:36||20:27:36|
|Second stage shutdown|
The first and second stages have placed the spacecraft, still connected to the third and the spent second stage, into orbit at an altitude of 190 kilometers (118 miles).
|Thrusters spin up the spacecraft to 50 revolutions per minute|
The spacecraft is spun in order to stabilize it for its onward journey.
|Second stage separation||0:04.0||21:37.0||16:31:08||20:31:08|
|Star 48 upper (third) stage ignition||0:37.0||22:14.0||16:31:45||20:31:45|
|Star 48 burnout|
The third and final rocket stage burns out at an altitude of only 278 kilometers (173 miles) above Earth. For the rest of the mission, Dawn will depend upon ions for all further changes to its trajectory.
|Spindown to zero|
A yo-yo despin system will counteract the spacecraft's spin. However, the xenon in the tank will still be spinning. Friction will eventually slow it down, but not before it has imparted some spin to the spacecraft.
|Third stage separation|
The spent third stage falls away at an altitude of 1,016 kilometers (631 miles).
|Thrusters counteract remaining spin|
After waiting a little more than 8 minutes for the liquid xenon to swirl to a stop, the spacecraft's hydrazine attitude-control thrusters will counteract whatever spin the spacecraft gained from the process.
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